The present invention relates to solar simulators, and more particularly to pulsed solar simulators. Even more particularly, the present invention relates to improved Large Area Pulsed Solar Simulators (LAPSS) and corresponding methods of testing multi-junction photovoltaic solar panels.
Spacecraft employ solar arrays to convert solar energy to the DC current needed to provide the necessary electrical power on-board the spacecraft. Consisting of large numbers of photovoltaic generators (also referred to as photovoltaic cells) arranged in rows and columns of a matrix on panels joined together into an essentially planar array, the solar array or panel is oriented toward the sun and converts the incident sunlight into electricity. To ensure that the individual photovoltaic generators within the array are functional, it is conventional to test the array and measure the performance of the photovoltaic generators prior to deployment in spacecraft. Any defective photovoltaic generators or cells found are conveniently replaced. A solar simulator is used for this test.
A Large Area Pulsed Solar Simulator (LAPSS) is known in the art as a test system for such photovoltaic generators positioned on large photovoltaic power panels, also referred to as photovoltaic panels or solar panels, using a pulsed light source, such as a Xenon flashlamp. Pulsed light from the flashlamp is directed at and illuminates the surface of the solar panel. The flashlamp is typically located away from the solar panel to be tested by a distance great compared to the dimensions of the solar panel. This ensures that the entire surface of the solar panel is uniformly illuminated. Typically, the standard LAPSS can test a solar panel about 10 to 15 feet square located at about 40 feet from the solar panel. The standard LAPSS uses one or two Xenon flashlamps that provide about 4,000,000 watts of power in about 1-2 msec flashes of light over a spectrum of at least 400-1800 nm, e.g. typically 180 nm to 2600 nm. Advantageously, the pulses of light simulate actual sunlight so that the effective performance of the solar panel can be measured prior to being placed in orbit on a satellite, for example. Thus, solar panels containing defective junctions (i.e. photovoltaic generators or solar cells) can be advantageously replaced prior to being placed into orbit.
LAPSS offers a significant improvement over multi-lamp continuous solar simulators, also referred to as steady state solar simulators, which are prohibitively expensive. Additionally, such steady state solar simulators cause the surface of the solar panel to xe2x80x9cheat upxe2x80x9d due to the exposure of the solar panel to the steady state light source; and thus, extensive cooling is needed to control the temperature on the solar panel. Such steady state solar simulators are typically used to test entire spacecraft, whereas the conventional LAPSS is used to test solar panels.
However, newer types of photovoltaic panels require a light source that matches the spectrum of sunlight over a wider range of wavelengths than are obtainable with the standard LAPSS. Such newer types of photovoltaic panels include multi-junction photovoltaic panels. For example, a multi-junction photovoltaic panel may consist of three separate junctions: a top junction responsive to light having a wavelength of 400-650 nm, a middle junction responsive to light having a wavelength of 650-850 nm, and a bottom junction responsive to light having a wavelength of 850-1800 nm. In the standard LAPSS, the Xenon flashlamps match the solar spectrum quite well in the spectral region from 400 nm to 1000 nm (with the proper selection of current level); however, such flashlamps are significantly deficient in the infrared (IR) spectral region longer than 1000 nm. For example, the energy in this spectral region, from 1000 nm to 1800 nm, is about one third as much as the energy of natural sunlight at one AM0 (i.e. air mass zero, which is the solar constant at the average earth distance from the sun expressed in units of watts per square meter) in this spectral region. As such, the newer multi-junction photovoltaic panels are not able to be accurately tested for response to the long IR spectral region of 1000 nm to 1800 nm using the standard LAPSS.
It is noted that large scale multi-lamp steady state test simulators can accurately test multi-junction photovoltaic devices; however, such simulators are prohibitively expensive and require extensive temperature control of the illuminated surfaces. What is needed is a pulsed solar simulator, e.g. LAPSS, that can more accurately match and simulate sunlight at one AM0 in the spectral region of 1000 nm to 1800 nm, as well as sunlight at one AM0 in the spectral region of 400 nm to 1000 nm, which is required for the accurate testing of multi-junction photovoltaic solar panels.
The present invention advantageously addresses the above and other needs.
The present invention advantageously addresses the needs above as well as other needs by providing an improved LAPSS that can accurately match and simulate sunlight at one AM0 in the spectral region from 400 nm to 1800 nm, such that the accurate testing of solar panels using multi-junction photovoltaic cells is possible.
In one embodiment, the invention can be characterized as a pulsed solar simulator comprising one or more mirrors and a flashlamp adjacent to the one or more mirrors. The flashlamp produces pulsed light beams comprising wavelengths from 400 nm to 1800 nm, wherein one or more primary pulsed light beams are directed at a target and one or more secondary pulsed light beams are directed at respective ones of the one or more mirrors and are directed toward the target as one or more reflected pulsed light beams by respective ones of the one or more mirrors. And, one or more respective spectral filters are positioned such that the one or more reflected pulsed light beams comprise light having a desired wavelength spectrum directed at the target. The one or more reflected pulsed light beams provide enhanced irradiation in the desired wavelength spectrum at the target compared to the irradiation provided by the one or more primary pulsed light beams alone.
In another embodiment, the invention can be characterized as a pulsed solar simulator comprising one or more mirrors and a flashlamp adjacent to the one or more mirrors. The flashlamp produces pulsed light beams comprising wavelengths from 400 nm to 1800 nm, wherein one or more primary pulsed light beams are directed at substantially an entire testing surface of a target and one or more secondary pulsed light beams are directed at respective ones of one or more mirrors and are directed toward substantially the entire testing surface of the target as one or more reflected pulsed light beams by the respective ones of the one or more mirrors. The one or more reflected pulsed light beams provide enhanced irradiation at substantially the entire testing surface of the target compared to the irradiation provided by the one or more primary pulsed light beams alone.
In yet another embodiment, the present invention may be characterized as a method of solar simulation for testing photovoltaic solar cells comprising the steps of: producing one or more primary pulsed light beams having wavelengths comprising 400 nm to 1800 nm emitted toward a target and one or more secondary pulsed light beams having the wavelengths comprising 400 nm to 1800 nm emitted away from the target; directing the one or more primary pulsed light beams toward a target; directing the one or more secondary pulsed light beams toward the target; filtering the one or more secondary pulsed light beams into a desired range of wavelengths; and irradiating the target with the one or more primary pulsed light beams and the one or more secondary pulsed light beams, wherein the one or more secondary pulsed light beams provide enhanced irradiation in the desired range of wavelengths compared to the irradiation provided by the one or more primary pulsed light beams alone.
In an additional embodiment, the invention can be characterized as a method of solar simulation for testing photovoltaic solar cells comprising the steps of: producing one or more primary pulsed light beams having wavelengths comprising 400 nm to 1800 nm emitted toward a target and one or more secondary pulsed light beams having the wavelengths comprising 400 nm to 1800 nm emitted away from the target; directing the one or more primary pulsed light beams toward substantially an entire testing surface of a target; directing the one or more secondary pulsed light beams toward substantially the entire testing surface of the target; and irradiating substantially the entire surface of the target with the one or more primary pulsed light beams and the one or more secondary pulsed light beams, wherein the one or more secondary pulsed light beams provide enhanced irradiation at substantially the entire testing surface of the target compared to the irradiation provided by the one or more primary pulsed light beams alone.